We developed and pilot-tested an overall protocol for intervention studies to evaluate the effects of indoor environmental changes in office buildings on the health symptoms and comfort of occupants. The protocol includes a web-based survey to assess the occupant's responses, as well as specific features of study design and analysis. The pilot study, carried out on two similar floors in a single building, compared two types of ventilation system filter media. With support from the building's Facilities staff, the implementation of the filter change intervention went well. While the web-based survey tool worked well also, low overall response rates (21-34% among the three work groups included) limited our ability to evaluate the filter intervention., The total number of questionnaires returned was low even though we extended the study from eight to ten weeks. Because another simultaneous study we conducted elsewhere using the same survey had a high response rate (>70%), we conclude that the low response here resulted from issues specific to this pilot, including unexpected restrictions by some employing agencies on communication with occupants.
In this small pilot study we were able to use formal statistical analyses for only two of six symptoms. Outdoor ozone above 58 ppb (a common level in Sacramento and many other cities in summer) was associated with a significant 64% increase in upper respiratory symptoms. This was consistent with a prior finding from a large U.S. study Otherwise the models showed only small non-significant changes in upper respiratory symptoms and eye symptoms in the predicted directions (increases with both synthetic filters and higher ambient ozone), and found no evidence for synergy between filters and outdoor ozone in their effects on symptoms.
Based on results of the pilot, we suggest revisions in future study protocols:
- Study only buildings that can provide email addresses for all occupants in the study spaces, and accurate counts of eligible employees there.
- Develop early and direct communication with employers and employee managers, in addition to facilities staff. To increase response rates, it will be helpful to develop support within each work group from one or more influential people ("champions"). Support from employee representatives (unions) where available may also be helpful.
- Tell participants exactly when to complete the surveys during each study period.
- Select alternate statistical approaches, such as different models or tests, to make the best use of the kind of data that the surveys produce.
The protocol should be usable for future intervention studies that assess the effects of changing the indoor environments of offices on occupant symptoms or comfort. Promising environmental factors to study, considered likely to influence the health or environmental satisfaction of occupants, in addition to reducing entry of outdoor pollutants such as ozone into indoor air, include ventilation rates, cleaning practices, and other aspects of the operation or maintenance of buildings. Estimates that we provide here on the frequencies of symptoms will also help in planning the necessary sizes of future studies.